This invention relates to a light source device having a discharge lamp used in a projection-type image display device or the like, and relates to the projection-type image display device using the light source device.
A light source device of an projection-type image display device includes a discharge lamp, a reflection mirror and a transparent plate. The discharge lamp, the reflection mirror and the transparent plate are housed in a case, and configured as one unit. Recently, in order to project a vivid image even in a well-lighted room, an output of the discharge lamp increases, and therefore it is demanded to enhance a cooling efficiency of the discharge lamp. Consequently, it is proposed to cool the discharge lamp by introducing the air into the interior of a reflection mirror through a cutout portion formed on the reflection mirror, as disclosed in, for example, Japanese Patent Publication No. HEI 8-314011 (see page 2 and FIG. 7).
FIG. 7 is a sectional view of a light source device disclosed in the above described publication. In the light source device, an exhaust fan 109 is provided on the rear side of a case 107 in which a discharge lamp 101 and a reflection mirror 102 are housed. When the exhaust fan 109 operates, the exhaust fan 109 causes the air to flow into the interior of the case 107 through the inlet opening 197a. The air flows through the interior of the case 107, and is discharged out of the case 107 through the bottom of the case 107. However, in such a cooling arrangement, a small amount of air flows along the rear side of the reflection mirror 102, and therefore it is difficult to sufficiently cool a rear part 101b of the discharge lamp 101 that protrudes rearward from the reflection mirror 102. Since the rear part 101b of the discharge lamp 101 highly influences the lifetime of the discharge lamp 101, it is demanded to solve this problem. Furthermore, since the difference in temperature between a reflection surface and a back surface of the reflection mirror 102 tends to be large, there is a possibility that the reflection mirror 102 may be broken.